Valve Drive for an Internal Combustion Engine

ABSTRACT

A valve drive for an internal combustion engine has a first camshaft which is rotatably mounted in a first and a second camshaft bearing and which includes at least one cam with a first cam curve and a second cam curve that differs from the first cam curve, wherein a gas exchange valve can be actuated by the first or the second cam curve. A camshaft section is provided, by which the cam can be moved by an actuator such that the gas exchange valve can be actuated either via the first or the second cam curve. The first camshaft and the cam have a fixed position relative to each other. The first camshaft can be axially moved in the first and the second camshaft bearing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT International Application No. PCT/EP2018/068925, filed Jul. 12, 2018, which claims priority under 35 U.S.C. § 119 from German Patent Application No. 10 2017 214 791.1, filed Aug. 24, 2017, the entire disclosures of which are herein expressly incorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a valve drive for an internal combustion engine.

Regarding the technical background, reference is made, for example, to European patent application EP 0 595 060 A1. This patent application discloses a valve drive of an internal combustion engine, which valve drive has prestressed sliding cams which can be displaced axially on a camshaft. In a first position, in which they act with a first lift lobe on inlet valves, the sliding cams can be displaced into a second position, in which they act with a second lift lobe on the inlet valves. In the first position, the sliding cams bear in an integrally joined manner against a stop of a transmission element which is connected between the inlet valves and the sliding cams, as long as they run with one section in the region of the stop. When the base circle of the sliding cams is reached, they are displaced into the second position.

A further example of sliding cams is known, for example, from German laid open specification DE 10 2005 006 489 A1. This is a camshaft arrangement which has a basic shaft and cam carriers which are arranged on it, and can be displaced axially but are held fixedly so as to rotate with the basic shaft. Here, cams with a plurality of cam lobes are configured on the cam carriers, which cams in each case have a common base circle and different cam lobes which have different lobe profiles than one another. Valve actuating means of associated cylinders are actuated by way of the cams. Actuators for carrying out switchover operations are provided, a different one of the cam lobes of the cam coming into contact with the valve actuating means in the case of the switchover operations by way of axial displacement of the cam carriers on the basic shaft.

German laid open specification DE 10 2004 022 833 A1 discloses a further valve drive for an internal combustion engine. The valve drive comprises a camshaft with a sliding cam device which has cam tracks, which lie next to one another and act on valves, with different cam shapes and lift lobes. The lift lobes interact with actuating elements which have control pins for the adjustment of the sliding cam device.

The known switching or sliding cams for multiple cylinder internal combustion engines have an externally splined drive shaft, on which internally splined sliding pieces are displaced axially. The manufacture of the spline systems is expensive and subject to tolerances, which, in addition to economic disadvantages, also involves acoustic disadvantages.

It is an object of the present invention to avoid the abovementioned disadvantages.

This and other objects are achieved according to the invention by a cylinder head of an internal combustion engine having a first camshaft which is mounted rotatably in a first and a second camshaft bearing with at least one cam with a first cam lobe and a second cam lobe which is different than the first cam lobe. A gas exchange valve is to be actuated by way of the first or the second cam lobe. A camshaft section is provided, by way of which the cam can be displaced via an actuator in such a way that the gas exchange valve can be actuated via either the first or the second cam lobe. The first camshaft and the cam have a fixed position with respect to one another, and the first camshaft can be displaced axially in the first and the second camshaft bearing.

The present invention provides considerable reductions in manufacturing costs, since no precise spline systems have to be manufactured. Undesired spline noise is also avoided.

According to further aspects, the cam and camshaft are in one piece and are made from the same material or the cam may be joined or shrunk-fit onto the camshaft.

By way of an embodiment in which the camshaft is hollow, the moving masses in the case of switchover operations are reduced considerably, with the result that substantially more rapid switching operations are possible.

In a further embodiment, the valve drive has a second camshaft which is mounted rotatably in a third and fourth camshaft bearing and is arranged in parallel with respect to the first camshaft. A first spur gearwheel is arranged radially around the first camshaft. The second spur gearwheel is arranged radially around the second camshaft. The first spur gearwheel and the second spur gearwheel are operatively connected to one another via a third spur gearwheel. Accordingly, the drive for an inlet-side and an outlet-side valve drive is possible.

In a further embodiment wherein the first camshaft has a plurality of cams with two cam lobes, and is provided for at least two cylinders of the internal combustion engine which are arranged inline, it is possible for internal combustion engines with a plurality of cylinders inline with a displaceable camshaft to be produced. This can be, for example, an inline two cylinder internal combustion engine, an inline three cylinder internal combustion engine or an inline four cylinder internal combustion engine, or else a V4 or V6 internal combustion engine.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a valve drive according to an embodiment of the invention for an internal combustion engine.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a plan view of a valve drive 1 for a cylinder head 16 of an internal combustion engine (not shown in greater detail).

The cylinder head 16 is shown without a valve cover, with the result that there is a clear view of the valve drive 1. The cylinder head 16 is provided for a four cylinder internal combustion engine, and has an inlet side with two first valve drives 1, of which only a single one is designated. On the outlet side, the cylinder head 16 has a single second outlet camshaft 12 for all four cylinders. On the inlet side, in each case one valve drive 1 is provided for in each case two cylinders. Only a single inlet-side valve drive is designated. The first camshaft 4 is mounted rotatably in a first and a second camshaft bearing 2, 3, only the bearing pedestals in the cylinder head 16 with non-designated screw bores being shown.

The first camshaft 4 has four cams 5, of which only one cam 5 is designated. The cam 5 has a first cam lobe 6 and a second cam lobe 7 which is different than the first cam lobe 6. A gas exchange valve (not shown) can be actuated by the first cam lobe 6 or by the second cam lobe 7 via an intermediate element (not shown), such as a sliding rocker arm.

Furthermore, a camshaft section 8 is provided, with radially circumferential, non-designated control grooves, by way of which the first camshaft 4 can be displaced axially in the camshaft bearings 2, 3 via an actuator 9, via a pin which protrudes into the control grooves. The first camshaft 4 can be displaced in such a way that, either via the first or the second cam lobe 6, 7, the cam 5 actuates the gas exchange valve via the intermediate element. Since the actuator 9 is known from the prior art, it is not described in greater detail.

According to the invention, the first camshaft 4 and the cam 5 have a fixed position with respect to one another, it being possible for the entire camshaft 4 to be displaced axially in the first and the second camshaft bearing 2, 3.

In a first embodiment, the cam 5 and the camshaft 4 are manufactured in one piece and from the same material, for example by way of casting with subsequent reworking. In a further embodiment, the cam 5 can also be joined or shrink-fitted onto the first camshaft 4. Manufacturing in a hydroforming method (internal high pressure forming) is also possible.

In one particularly preferred embodiment, the camshaft 4 is hollow, in order to reduce the moving masses, which makes substantially more rapid switching operations by way of the actuator 9 possible.

In comparison with the known prior art, the entire camshaft 4 is therefore displaced axially, with the result that two different cam lobes 6, 7 of the cam 5 are operatively connected alternately to the gas exchange valve. It is also possible for more than two cam lobes 6, 7 to be provided.

The concept according to the invention therefore provides considerable reductions in the manufacturing costs, since no precise axial spline systems have to be manufactured. Undesired spline noise is also advantageously avoided completely, which leads to a considerable improvement in the acoustics. Therefore, the valve drive 1 according to the invention is suitable both for two-wheeled vehicles, such as mopeds and motorcycles, and for motor vehicles of all types.

Furthermore, as has already been described, the valve drive 1 has, on the outlet side, a second camshaft 12 which is arranged in parallel with respect to the first camshaft 4 and is mounted rotatably in a third and a fourth camshaft bearing 10, 11 and two further, non-designated camshaft bearings. On the end side, the first camshaft 4 has a first spur gearwheel 13 which extends radially around the camshaft 4, and the second camshaft 12 has a second spur gearwheel 14 which extends radially around the second camshaft 12, the first spur gearwheel 13 and the second spur gearwheel 14 being operatively connected to one another via a third spur gearwheel 15. The same mechanism is situated at the other end of the second camshaft 12 in a mirror-inverted manner, in order to drive the second, non-designated, inlet-side first camshaft. In this way, a phase-locked drive is possible both on the inlet side and on the outlet side.

According to the invention, a sliding camshaft is therefore shown instead of a sliding cam. The concept according to the invention therefore provides considerable reductions in the manufacturing costs, since no precise axial spline systems have to be manufactured. Undesired spline noise is also avoided.

LIST OF DESIGNATIONS

-   1 Valve drive -   2 First camshaft bearing -   3 Second camshaft bearing -   4 First camshaft -   5 Cam -   6 First cam lobe -   7 Second cam lobe -   8 Camshaft section -   9 Actuator -   10 Third camshaft bearing -   11 Fourth camshaft bearing -   12 Second camshaft -   13 First spur gearwheel -   14 Second spur gearwheel -   15 Third spur gearwheel -   16 Cylinder head

The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 

What is claimed is:
 1. A valve drive for a cylinder head of an internal combustion engine, comprising: a first camshaft mounted rotatably in a first and a second camshaft bearing, wherein the first cam shaft has at least one cam with a first cam lobe and a second cam lobe which is different than the first cam lobe, a gas exchange valve being actuatable by way of the first or the second cam lobe, the first camshaft has a camshaft section by way of which the cam is displaceable via an actuator such that the gas exchange valve is actuatable via either the first or the second cam lobe, the first camshaft and the cam have a fixed position with respect to one another, and the first camshaft is displaceable axially in the first and the second camshaft bearing.
 2. The valve drive according to claim 1, wherein the cam and the camshaft are in one piece and are made from the same material.
 3. The valve drive according to claim 1, wherein the cam is joined or shrunk-fit onto the camshaft.
 4. The valve drive according to claim 1, wherein the camshaft is hollow.
 5. The valve drive according to claim 1, further comprising: a second camshaft mounted rotatably in a third and a fourth camshaft bearing and arranged in parallel with respect to the first camshaft; a first spur gearwheel arranged radially around the first camshaft; a second spur gearwheel arranged radially around the second camshaft; and a third spur gearwheel by which the first spur gearwheel and the second spur gearwheel are operatively connected to one another.
 6. The valve drive according to claim 1, wherein the first camshaft has a plurality of cams each having two cam lobes, and the first camshaft is provided for at least two cylinders of the internal combustion engine which are arranged inline. 